Athena Forensics - Computer Forensics NewsClick here to return to our News index
A mobile phone can be traced by its digital fingerprint
Tech-savvy criminals try to evade being tracked by changing their mobile phone's built-in ID code and by regularly dumping SIM cards. But Researchers at the Dresden University of Technology have discovered that the radio signal from every mobile phone handset hides within it an unalterable digital fingerprint - potentially giving law enforcers a simple way of tracking the handset itself.
The tracking method can remotely identify individual GSM phones based on unique characteristics in their radio signals. The radio hardware in a mobile phone consists of a collection of components like power amplifiers, oscillators and signal mixers that can all introduce radio signal inaccuracies. A phone's resistance, for of instance, can vary between 0.1 and 20 per cent its stated value depending on the quality of the component.
The upshot of these errors is that when analogue signals are converted into digital phone ones, the stream of data each phone broadcasts to the local mast contains error patterns that are unique to that phone's peculiar mix of components. In tests on 13 handsets in their lab, the Dresden team were able to identify the source handset with an accuracy of 97.6 per cent. An impressive initial result, that the team behind the work say is just the first step in this type of remote mobile phone forensics.
The method does not send anything to the mobile phones. It works completely passively and just listens to the ongoing transmissions of a mobile phone - it cannot be detected. Their research, funded by the EU and the German government, was performed on 2G phones. The team state that defects are present in every radio device, so it should also be possible to replicate this with 3G and 4G phones.
The novel method is welcome but technically demanding, say forensics specialists. However serious criminals are extremely adept in using single-use phones and dumping SIM cards so new capabilities like this would certainly help law enforcement.
Identifying a phone from its radio frequency fingerprint is certainly not far-fetched. It is similar to identifying a digital camera where the image metadata does not provide a serial number. From underlying imperfections in the lens, which are detectable in the image, the source camera can be identified.